Process for producing an improved cutting tool

ABSTRACT

The sharpened edge of a cutting implement such as a razor blade is modified by depositing a layer of dielectric material on the cutting edge and then depositing a layer of electrically conductive material on the dielectric layer and then subjecting the cutting edge to DC ion bombardment so that a portion of the deposited electrically conductive material is removed and the dielectric material is exposed at the tip of the implement.

[11] 3,811,189 May 21, 1974 United States Patent 1191 Sastri 3,632,4941/1972 Herte et 3,743,551 7/1973 Sanderson 3,754,329

8/1973 Lane....................... 30/346.53

Aiyaswami S. Sastri, Stow, Mass.

FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee: The G'lletecompanyBostonMass' 1,030,401 5/1966 Great Britain,..................30/346.55 [22] Filed:

Mar. 19, 1973 Primary Examiner-Al Lawrence Smith Assistant Examiner-J.C. Peters [21] Appl. N0.: 342,754

Related US. Application Data [62] Division of Ser. No. 161

,159, July 9, 1971, Pat. No.

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3 345 202 10/1967 Kiss et al. 30/346.53 x 3,480,483 11/1969Wilkinson1.......,................ 204/192 5 Claims, 3 Drawing FiguresPATENTEDHAYZI 1914 FIG i FIG 3 FIG 2 PROCESS FOR PRODUCING AN IMPROVEDCUTTING TOOL This application is a division of Ser. No. 161,159, filedJuly 9, 1971, entitled Process for Producing an Improved Cutting Tool,"now US. Pat. No. 3,761,373.

SUMMARY OF INVENTION This invention relates to processes for producingan extremely sharp and durable cutting edge on a razor blade or similarcutting tool, and to improved cutting tools.

The forming of the cutting edges of razor blades by mass productiontechniques conventionally involves a series of abrading operations(grinding and honing) to produce the desired sharp and durable shavingedge. Each abrading operation forms a facet on the blade edge beingsharpened, which facet is modified by subsequent abrading operations ofincreasing fineness. In general, the blade edge configuration is a wedgeshape, the included solid angle of which is typically 2030. The faces orsides of such cutting edges may extend back from the ultimate edge adistance up to as much as 0.1 inch or even more. Each face need not be asingle uninterrupted continuous surface or facet, but may consist of twoor more facets formed by successive grinding or honing operations andintersecting each other along zones generally parallel to the ultimateedge. The final facet, i.e., the facet immediately adjacent the ultimateedge, has a width as low as 7.5 microns or even less compared with thediameter-of beard hair which averages about 100 to 125 microns. Throughshave test evaluation and measurement of the geometry of such sharpenedcutting edges, it has been found that the cutting edge should have anaverage tip radius of less than 500 Angstroms. A thin adherent layer ofa corrosion resistant metal is often applied to the cutting edge of theblade. Further, a shave facilitating layer of polymeric material is alsofrequently applied to the blade edge. These layers must have adhesioncompatability so that they remain firmly adhered to one another and tothe substrate throughout the life of the cutting tool and not adverselyaffect the edge geometry.

It is a general object of this invention to provide novel and improvedcutting implements, the cutting edges of which have improved mechanicalproperties.

Another object of the invention is to provide novel and improvedprocesses for producing improved cutting tools.

A further object of the invention is to provide novel and improved razorblades which possess superior shaving properties.

In accordance with the invention, the edge geometry of a cuttingimplement such as a razor blade is modified by a process which includesthe steps of forming a cutting edge of dielectric material, depositing alayer of electrically conductive material on said dielectric material,and then subjecting the composite cutting edge to a DC ion bombardmentstep so that a portion of the deposited electrically conductive materialis removed so that the dielectric material is exposed at the ultimatetip.

In particular embodiments, the cutting edge is formed in a metalsubstrate by a suitable procedure such as grinding, honing, stropping,chemical etching, electrolytic sharpening, or forming with anappropriately shaped die; and then the edge is subjected to twosuccessive strengthening material deposition steps, the first stepdepositing a layer of dielectric material and the second step depositingthe layer of electrically conductive material. Preferably the layers aredeposited by sputtering on a multiplicity of blade elements while theblade edges are disposed in parallel alignment with one another and in aplane parallel to a target member spaced from the blade edges. A planartarget member is used in one embodiment while a cylindrical target rodis used in another embodiment.

A razor blade in accordance with the invention has an average tip radiusof less than 500 Angstroms, the exposed tip material is a dielectric,such as A1 0 and added strengthening metal, such as chromium or achrome-platinum alloy, is on the flanks of the cutting edge. Such razorblades exhibit excellent shaving characteristics and have a long shavinglife. A wide range of blade substrate materials may be used, specificrazor blade steel compositions with which the invention may be practicedincluding the following:

COMPOSITION IN C Cr Mo Si Ni Other objects, features and advantages ofthe invention will be seen as the following description of particularembodiments progresses, in conjunction with the DESCRIPTION OFPARTICULAR EMBODIMENT Diagrammatically shown in FIG. 1 is a sputteringapparatus which includes a stainless steel chamber 10 having wallstructure 12 and a base 14 in which is formed a port 16 which is coupledto a suitable vacuum system (not shown). Mounted in chamber 10 is asupport 18 on which is disposed a stack of razor blades 20 and supportstructures 22, 24 for target member 26 of dielectric material and target28 of electrically conductive material. Support structures 18, 22 and 24are electrically isolated from chamber 10 and electrical connections areprovided to connect blade stack 20 and targets 26, 28 to appropriateenergizing apparatus 30, 32, 34. It will be understood that this is adiagrammatic showing of suitable apparatus. In one embodiment thetargets 26, 28 are horizontally disposed discs, each 6 inches indiameter and one-quarter inch thick; and 4 U2 inch long stack of blades20 is placed on a 5 inch diameter aluminum support disc 18 disposedparallel to target discs 26, 28. Disc 18 is movable between a firstposition aligned with target 26 and a second position aligned withtarget 28. A coil of razor blade strip may be similarly positioned onsuch a support with its sharpened edges defining a plane exposed toparallel to targets 26, 28. In another embodiment, target rod that hasan exposed length of 29 inches and is 1 1/4 inches in diameter isemployed. Suitable coolant is circulated through the rod for coolingpurposes. A series of stacks of razor blades (either in coil form or intwelve inch long axial extending stacks) are disposed about, the targetrod at equal distances therefrom.

The geometry of the edge of a typical razor blade of commercial qualitysharpened by conventional abrading techniques is shown in F IG. 2 at amagnification of about 100,000 times. The tip 40 has a radius that istypically in the range of 125-500 Angstroms, a typical average radius(the average of radius measurements taken at 5 to points along thelength of the blade edge) being about 2 50 Angstr0nts. The Wlilank width(at a distance of 1,000 Angstroms fr om the u ltim ate edge 40) istypically in the range of 1,200 to 1,400

Angstroms. The W2 width (at a distance of 2,000 Ang- 1 strorns from thetip 40) is about 2,100 Angstroms; the W4 width (at a distance of 4,000Angstroms from the tip 40) is about 3,200 Angstroms; the W6 width (at adistance of 6,000 Angstroms) is about 4,100 Angstroms; and the W8 width(at a distance of 8,000 Angstroms from the tip) is about 5,100Angstroms.

These measurements were made by a high resolution electron microscopytechnique in which a magnified image of a blade edge profile(silhouette) is photographed. The blades are cleaned by immersion intrichloroethylene; subjection to ultrasonic cleaning for 2 minutes;rinsing in a mixture of one-half acetone and one-half methanol; cleanedin warm air; and then demagnetized in a solenoid coil. A blade specimenin the order of one square millimeter in size with four sides, one ofwhich is the original sharpened razor blade edge, is obtained byabruptly snapping the blade with the help of a suitable instrument suchas a watchmakers plier. The blade may be snapped in air or if the bladewill-not break readily in liquid nitrogen (at a temperature below theductile to brittle transition value).

A 100 KV RCA EMU4 electron microscope is used with a standard air lockspecimen holder modified to accommodate the small blade edge fragment.The microscope was fitted with a liquid nitrogen cooled bafile valve toreduce contamination during photography. The blade edge profile is heldin the path of the electron beam so that a shadow image of the ultimatetip is cast on the final viewing screen. The magnification of the finalimage is controlled by the strength of the intermediate lens current andthe focusing is achieved with control of the objective lens current. Themicroscope magnification was calibrated in terms of focusing lenscurrent.

The tip radius of the resulting photomicrograph was measured by fitting90 arcs of circles to the tip profile and selecting as the tip radiusthat edge profile that best fits the profile of the photomicrograph. Thepoint to point resolution of the microscope is in the order of 5Angstroms. The variation and average radius of a large number of edgesfrom a particular batch of blades using this technique was within i 12.5Angstroms. The W1, W2 and other dimensions are similarly measured fromthe photomicrograph.

in operation of the apparatus shown in F 1G. 1, sharpened blades 20 aredisposed in a stack with their sharpened edges aligned and are placed inchamber 10 on support 18. The chamber is evacuated and the blade edgesare subjected to ion bombardment, for example by a glow dischargemaintained in argon at a pressure of ten microns to modify the edgegeometry as generally indicated byline 42 in FIG. 2 and specifically toreduce the tip radius, a typical radius reduction being about Angstroms.The chamber is again evacuated and argon at a pressure of 5-8 microns isplaced in the chamber. With the blade stacks and chamber grounded, an RFpotential is applied to dielectric target 26 and argon ions are producedwhich bombard target 26 and release atoms of the target material. Thereleased atoms of dielectric material are deposited on exposed surfaces,including the sharpened blade edges. This layer is applied uniformly tothe thickness of less than 500 Angstroms. The support 18 is then alignedwith target 28 and an RF potential applied to that target to causedeposition of an electrically conductive layer on the dielectric layer.The RF power supply is then disconnected from the target 28and theblades are subjected to DC ion bombardment. which removes electricallyconductive but not dielectric material, more material being removed fromthe tip region of the blades than the flanks. The resulting blades havea cutting edge geometry of the nature diagrammatically indicated in FlG.3 in which the exposed tip 44 is dielectric material and its averageradius is about-250 Angstroms and two layers 46, 48 are on the flanks atthe W6 dimension.

As a specific example, a 4 1/2-inch long stack of stainless steel razorblades having the following composition:

carbon 0.54-0.62% chromium 13.5-14.S% manganese 0.20-0.S0% silicon0.20O.50% phosphorus, max. 0.025% sulphur, max. 0.020% nickel, max.0.50% max. iron remainder and sharpened to the edge geometry asindicated in FIG. 2, were placed on a 5 inch diameter aluminum discsupport 18 in an RF sputtering unit. Two targets were employed, an A1 0target 26, and a Cr Pt target 28. The A1 0 target 26 was a sinteredcompact disc six inches in diameter and 1/4 inch thick, and the Cr Pttarget 28 was a pure chromium disc 6 inches in diameter and 1/4 inchthick that had squares of pure platinum foil one centimeter on a sideand 0.002 inch thick spot welded on its surface. The foil squares werespaced on the surface so that 23 percent of the chromium surface wascovered with platinum. The target surfaces were disposed parallel to thesharpened blade edges at a distance of 2 112 inches from those edges.

Pressure in the vacuum chamber 10 was reduced to 0.1 micron of mercuryand then pure argon gas was bled into the chamber to a pressure of tenmicrons of mercury. The aluminum support disc 18 was then connected to aDC source of power and with the chamber 10 grounded the blade edges weresubjected to ion bombardment at a voltage of 1,800 volts and a currentof 35 milliamperes for seven minutes. The targets 26,

28 were covered by metal shields during this step. A

13.56 magahertz RF source was connected to A1 0 target 26 and thattarget was sputtered for thirty minutes while maintaining ten microns ofmercury pressure or argon gas in the chamber. The shield was thenremoved from between the blades 20 and the target 26 and 0.4 kilowattsof power (with a DC negative bias of about 3,400 volts and asuperimposed RF signal of 5 about 4,500 volts peak to peak) was appliedfor 1 minutes while maintaining argon at 10 micrions pressure. The edgesof the blades facing target 26 received an aluminum oxide layer 46 to athickness of about 250 Angstroms. Application of RF power was thenterminated and support 18 was aligned with the Cr Pt target 28. The CrPt target 28 was connected to the RF source and cleaned for five minutesand then a layer 48 of chromium-platinum alloy 250 Angstroms inthickness was deposited by application of 0.4 kilowatts of power for 75seconds. The blade stack was then connected to the DC source andsubjected to ion bombardment for seven minutes at 1,800 volts atacurrent of 100 milliamperes to remove the chromium-platinum film fromthe tip region but not the flank region of the blades to provide a bladeedge geometry as shown in FIG. 3. The resulting blades have an averagetip radius of 250 Angstroms, an average W1 dimension of about 1,400Angstroms, a W2 dimension of about 2,500 Angstroms, a W4 dimension ofabout 4,000 Angstroms, and a W6 dimension of about 5,150 Angstroms. Acoating of polytetrafluoroethylene telomer was then applied to the edgesof the blades in accordance with the teaching in US. Pat. No. 3,518,110.This processing involved heating the blades in an argon environment andprovided on cutting edges of the razor blades an adherent coating ofsolid PTFE. These blades exhibited excellent shaving properties and longshaving life.

It will be understood that a variety of dielectric materials includingother metal oxides may be used for the dielectric layer 46 and thatother metals and metal alloys may be used for the electricallyconductive layer 48. lon bombardment between the application of thedielectric and conductive layers is optional. For exam- 6 ple, such ionbombardment may be desirable when the process is employed with separatedeposition chambers with a single target in each chamber.

The invention provides an improved cutting implement such as a razorblade in which the tip radius of the implement is within the optimumrange for cutting effectiveness, the exposed tip is of dielectricmaterial and substantial amounts of edge strengthening materials havebeen added to the flanks of the cutting edge.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiment or to details thereof anddepartures may be made therefrom within the spirit and scope of theinvention.

What is claimed is:

l. A cutting implement having an average tip radius of less than 500Angstroms, said cutting implement comprising a metal substrate having acutting edge with a tip radius of less than 500 Angstroms, a layer ofdielectric material on the tip and flanks of said cutting edge, thethickness of said dielectric layer being in the range of about -300Angstroms, the exposed tip of said cutting implement being of saiddielectric material and a layer of electrically conductive strengtheningmetal on said dielectric material on the flanks of said cutting edge.

7 2. The cutting implement as claimed in claim 1 wherein said dielectricmaterial is a metal oxide.

3. The cutting implement as claimed in claim 2 wherein said metal oxideis aluminum oxide.

4. The cutting implement as claimed in claim 3 wherein said electricallyconductive layer includes chromium.

5. The cutting implement as claimed in claim 1 wherein said cuttingimplement is a razor blade.

1. A cutting implement having an average tip radius of less than 500Angstroms, said cutting implement comprising a metal substrate having acutting edge with a tip radius of less than 500 Angstroms, a layer ofdielectric material on the tip and flanks of said cutting edge, thethickness of said dielectric layer being in the range of about 100-300Angstroms, the exposed tip of said cutting implement being of saiddielectric material and a layer of electrically conductive strengtheningmetal on said dielectric material on the flanks of said cutting edge. 2.The cutting implement as claimed in claim 1 wherein said dielectricmaterial is a metal oxide.
 3. The cutting implement as claimed in claim2 wherein said metal oxide is aluminum oxide.
 4. The cutting implementas claimed in claim 3 wherein said electrically conductive layerincludes chromium.
 5. The cutting implement as claimed in claim 1wherein said cutting implement is a razor blade.